van der Waals semiconductors have proven to be exceptional for electronic and photonic applications. Although most research is extensively focused on some transition metal dichalcogenides materials (MX 2 ) such as MoS 2 , WS 2 , WS e2 , and MoSe 2 , studies on 2D metal monochalcogenides such as germanium sulfide (GeS) has been widely under investigated, mainly due to the high contact resistance GeS devices exhibit. Here, a van der Waals field-effect transistor (VdW-FET) based on GeS is investigated and resonant tunneling behavior is shown at room temperature due to VdW doping via black phosphorus (BP), evident by the observation of multiple decades of negative differential resistance (NDR) during doping transient state. These NDR decades are caused by confinement of carriers inside the double barrier quantum well, which allows tunneling to occur for discrete energy levels. Moreover, a noticeable conductivity switch from a low p-type to a high n-type is observed, with a conductivity enhancement of 2 orders of magnitude compared to pristine GeS devices. The underlying mechanism behind the observed NDR and the conductivity switch is discussed and it is shown that these phenomena are likely caused by phosphorus doping due to BP sublimation, evident by the detected P-Ge Raman peak in the measured Raman spectra. The results can open doors for electrical oscillators and switching devices for the next generation of nanoelectronics.

Recent reports on thermal and thermoelectric properties of emerging 2D materials have shown promising results. Among these materials are Zirconium-based chalcogenides such as zirconium disulfide (ZrS 2 ), zirconium diselenide (ZrSe 2 ), zirconium trisulfide (ZrS 3 ), and zirconium triselenide (ZrSe 3 ). Here, the thermal properties of these materials are investigated using confocal Raman spectroscopy. Two different and distinctive Raman signatures of exfoliated ZrX 2 (where X = S or Se) are observed. For 2D-ZrX 2 , Raman modes are in alignment with those reported in literature. However, for quasi 1D-ZrX 2 , Raman modes are identical to exfoliated ZrX 3 nanosheets, indicating a major lattice transformation from 2D to quasi-1D. Raman temperature dependence for ZrX 2 are also measured. Most Raman modes exhibit a linear downshift dependence with increasing temperature. However, for 2D-ZrS 2 , a blueshift for A1g mode is detected with increasing temperature. Finally, phonon dynamics under optical heating for ZrX 2 are measured. Based on these measurements, the calculated thermal conductivity and the interfacial thermal conductance indicate lower interfacial thermal conductance for quasi 1D-ZrX 2 compared to 2D-ZrX 2 , which can be attributed to the phonon confinement in 1D. The results demonstrate exceptional thermal properties for Zirconium-based materials, making them ideal for thermoelectric device applications and future thermal management strategies.

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